Quantitative interpretation of magnetic field measurements in eddy current defect detection

Abstract

For many years, the theoretical and experimental study of eddy current non-destructive evaluation (NDE) has been conducted separately, as most models were not suited to practical industrial applications. The aim of this work is to bridge this gap by investigating the relationship between magnetic fields and defects using both modelling and experimental study and to link these results to quantitative NDE. In this work, 3D FEM numerical simulations are used to predict the response of an eddy current probe being scanned over the area of a defect and understand the underlying change in magnetic field due to the presence of the defect. Experimental investigations are performed to study the feasibility of the proposed magnetic field measurement techniques for defect detection. This experimental work investigates the inspection of both surface and subsurface defects, the use of rectangular (directional) probes and the measurement of complex magnetic field values, as the response in these cases has been found to have a greater correlation with the shape of the defect being studied. As well as the detection of defects, both frequency spectrum and transient information from pulsed eddy current responses are used to reconstruct the profile (depth and width) of a slot shaped defect. The work concludes that the use of magnetic field measurements provides useful information for defect detection and quantification. This will have applications in both industrial and research areas, including visualisation of defects from magnetic field measurements, which can be applied to the monitoring of safety critical components.